Analysis of Blanks
Blank (i): The sentence states that the first steps of human progress are "irregular and (i) _______ ," contrasting with the smooth, waste-free "one step leads to another" model presented first. The word needed must suggest difficulty, hesitation, or instability.
- A. catastrophic: Too extreme for a general description of early human progress.
- B. dramatic: Implies striking, sudden change, which contradicts the "long period of readjustment."
- C. faltering: Hesitant, unsteady, or losing momentum. This pairs well with "irregular" to describe an unstable beginning.

Blank (ii): The sentence structure is: "a movement forward here and a (ii) ______ force there." The second half must contrast or modify the forward movement, indicating the irregularity and difficulty. The force must slow or hold things back.
- D. retarding: Causing a delay or slowing down the progress of something. This perfectly contrasts with "movement forward" and fits the theme of irregular, uneven progress.
- E. dominating: Doesn't fit the context of movement opposition.
- F. impulsive: Describes a sudden drive, not a sustained opposing force.

Blank (iii): A tribe making a special discovery gains "power over others." The blank needs a term meaning a position of dominant power or influence.
- G. echelon: A level or rank, often within a formation. (Too specific/neutral.)
- H. nadir: The lowest point. (Opposite of what is required.)
- I. ascendancy: The state of being in a position of power or influence. This aligns perfectly with "gives it power over others."